On Tue, 2007-04-17 at 21:43 +0200, Miklos Szeredi wrote: > > > > I'm a bit lost about what is currently done and who advocates for what. > > > > > > > > It seems to me the MNT_ALLOWUSERMNT (or whatever :) flag should be > > > > propagated. In the /share rbind+chroot example, I assume the admin > > > > would start by doing > > > > > > > > mount --bind /share /share > > > > mount --make-slave /share > > > > mount --bind -o allow_user_mounts /share (or whatever) > > > > mount --make-shared /share > > > > > > > > then on login, pam does > > > > > > > > chroot /share/$USER > > > > > > > > or some sort of > > > > > > > > mount --bind /share /home/$USER/root > > > > chroot /home/$USER/root > > > > > > > > or whatever. In any case, the user cannot make user mounts except under > > > > /share, and any cloned namespaces will still allow user mounts. > > > > > > I don't quite understand your method. This is how I think of it: > > > > > > mount --make-rshared / > > > mkdir -p /mnt/ns/$USER > > > mount --rbind / /mnt/ns/$USER > > > mount --make-rslave /mnt/ns/$USER > > > mount --set-flags --recursive -oallowusermnt /mnt/ns/$USER > > > chroot /mnt/ns/$USER > > > su - $USER > > > > > > I did actually try something equivalent (without the fancy mount > > > commands though), and it worked fine. The only "problem" is the > > > proliferation of mounts in /proc/mounts. There was a recently posted > > > patch in AppArmor, that at least hides unreachable mounts from > > > /proc/mounts, so the user wouldn't see all those. But it could still > > > be pretty confusing to the sysadmin. > > > > unbindable mounts were designed to overcome the proliferation problem. > > > > Your steps should be something like this: > > > > mount --make-rshared / > > mkdir -p /mnt/ns > > mount --bind /mnt/ns /mnt/ns > > mount --make-unbindable /mnt/ns > > mkdir -p /mnt/ns/$USER > > mount --rbind / /mnt/ns/$USER > > mount --make-rslave /mnt/ns/$USER > > mount --set-flags --recursive -oallowusermnt /mnt/ns/$USER > > chroot /mnt/ns/$USER > > su - $USER > > > > try this and your proliferation problem will disappear. :-) > > Right, this is needed. > > My problem wasn't actually this (which would only have hit, if I tried > with more than one user), just that the number of mounts in > /proc/mounts grows linearly with the number of users. > > That can't be helped in such an easy way unfortunately. > > > > Propagating some mount flags and not propagating others is > > > inconsistent and confusing, so I wouldn't want that. Currently > > > remount doesn't propagate mount flags, that may be a bug, > > > > For consistency reason, one can propagate all the flags. But > > propagating only those flags that interfere with shared-subtree > > semantics should suffice. > > I still don't believe not propagating "allowusermnt" interferes with > mount propagation. In my posted patches the mount (including > propagations) is allowed based on the "allowusermnt" flag on the > parent of the requested mount. The flag is _not_ checked during > propagation. > > Allowing this and other flags to NOT be propagated just makes it > possible to have a set of shared mounts with asymmetric properties, > which may actually be desirable. The shared mount feature was designed to ensure that the mount remained identical at all the locations. Now designing features to make it un-identical but still naming it shared, will break its original purpose. Slave mounts were designed to make it asymmetric. Whatever feature that is desired to be exploited; can that be exploited with the current set of semantics that we have? Is there a real need to make the mounts asymmetric but at the same time name them as shared? Maybe I dont understand what the desired application is? RP > > Miklos - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
